Nigerian Eocene Mollusca. 57 



Sinum afrioanum, sp. nov. 

 PLATE 4, fig. 12, 13. 



DESCRIPTION. Shell oval, very slightly arched, depresso-convex, auriform ; 

 spire small, lateral, depressed, with smooth protoconchal region consisting of 

 three volutions furnished with a minutely canaliculated suture, and an obtuse 

 apex ; aperture shallow ovately elongate, oblique, with excavated columella lip 

 and a nearly vertically margined labrum ; umbilicus present, but only exposed 

 when the thin callosity covering has been removed ; sculpture of minute texture, 

 consisting of numerous, moderately distant, spiral ridges with irregularly serrated 

 margins, divided by smooth furrows and crossed at intervals by strong concentric 

 growth periods. 



DIMENSIONS. 



Alt. ... ... ... ... ... ... ... 15 millimetres 



Lat. 10 



Depth ... 5 



REMARKS. This Gastropod belongs to the very depressed forms of Naticoid 

 shells which Bolten : recognised under the genus Sinum in 1798, Lamarck 2 as 

 Sigaretus in 1799, and de Blainville 3 as Cryptostomus in 1818. This species is 

 much flatter than any members of the genus found in Eocene rocks, such as 

 S. clathratus, &c., which are more or less conically shaped, of rounder periphery 

 and bearing an elevated spiral region. It exhibits characters which connect it 

 more with shells of the Miocene, Pliocene and Recent seas, in which the earliest 

 volutions are generally on the same plane as the body-whorl. This species 

 is represented by four specimens of very similar size, although, unfortunately, 

 one of the better examples illustrated in the plate has been recently broken 

 beyond repair, and only its fragments deposited in a glass test-tube, are now 

 available for study. 



OCCURRENCE. Cuttings Nos. 6, 10. 

 COLLECTOR. Mr. Kitson. 



1 Museum Boltenianum, 1798, p. 14. Type = Helix haliotoideus, Linnaeus. 



2 Mem Soc. Hist. Nat. Paris, 1799, P- 77- Type = H. haliotoideus, Linnaeus. 



3 Bull. Sci. Soc. Philom. Paris, 1818, pp. 120-122, and Manuel de Malacologie, 1827, p. 467, pi. 42, 

 fig- 3-. Type Cryptostomus leachi, de Blainville. This type is stated in the 181 8 memoir to be among 

 the spirit specimens at the British Museum. 



